Preheating of oil shale prior to pyrolysis

Abstract

A process for preheating oil shale in which the oil shale is partially preheated to 200° F. to 400° F. in a first lift pipe followed by final preheat to temperatures of between 400° F. and 650° F. in a second lift pipe. Hydrocarbons released from the oil shale in both the first and second lift pipes are incinerated in an incinerator/recuperator. In order to provide adequate incineration and combustion of the hydrocarbons released in the first, low temperature lift pipe, the entrainment gas or first gas stream is a low Btu gas preferably produced from conventional gasification of carbonaceous material. The low Btu entrainment gas along with released hydrocarbons is utilized as a fuel in the incinerator/recuperator and also may be utilized for other combustion applications in oil shale pyrolysis processing. In oil shale pyrolysis carried out with ceramic balls as heat exchange bodies, a portion of the low Btu entrainment gas is conveniently utilized to fuel the ball heater. The heat generated in the incinerator/recuperator, is utilized to preheat various process gases to thereby recover and recuperate the heating value of the hydrocarbons released during preheat.

What is claimed is: 
     
       1. A process for partially preheating oil shale to a temperature of between about 200° F. and 400° F. comprising: entraining raw oil shale in a substantially oxygen free combustible gas stream having a sufficient temperature to raise the temperature of said raw oil shale to between about 200° F. and 400° F. to form partially preheated oil shale and a partially cooled combustible gas stream having hydrocarbons released from the oil shale entrained therein;   separating the partially preheated oil shale from the partially cool gas stream;   transferring the separated partially preheated oil shale to apparatus for further preheating and pyrolysis; and   utilizing said first gas stream as a combustion fuel whereby said hydrocarbons released from said raw oil shale entrained therein are combusted with said partially cooled gas stream and not vented to the atmosphere.   
     
     
       2. A process according to claim 1 wherein said combustible gas stream is a low Btu gas produced by gasification of carbonaceous material. 
     
     
       3. A process according to claim 2 in which said carbonaceous material is auxiliary oil shale. 
     
     
       4. A process for preheating oil shale to a temperature of between about 400° F. and 650° F. comprising the steps of: entraining raw feed oil shale in a low Btu gas to partially preheat said raw feed oil shale to a temperature of between about 200° F. to 400° F.;   separating said partially preheated feed oil shale from said low Btu gas said low Btu gas having hydrocarbons entrained therein;   entraining said partially preheated feed oil shale in a hot preheat gas stream to preheat said partially preheated feed oil shale to a temperature of between about 400° F. and 650° F.;   separating the preheated feed oil shale from the hot preheat gas stream to form preheated oil shale and preheat flue gas, said preheat flue gas containing hydrocarbons released from said feed oil shale;   passing said flue gas and said low Btu gas to an incineration zone; and   adding sufficient combustion air to said incineration zone to combust the low Btu gas and the hydrocarbons in said low Btu gas and said preheat flue gas to form a substantially hydrocarbon free waste gas and combustion heat.   
     
     
       5. A process according to claim 4 wherein auxiliary raw oil shale is gasified to produce said low Btu gas. 
     
     
       6. A process according to claim 5 wherein said gasification of auxiliary raw oil shale is carried out in a pressurized fluid bed gasifier to produce a low Btu gas having a temperature of between about 1300° F. and 1500° F. 
     
     
       7. A process according to claim 6 wherein the low Btu gas has a heating value of between about 100 and 150 Btu/SCF (HHV). 
     
     
       8. A process according to claim 5 wherein said hot preheat gas stream is at a temperature of between about 1300° F. and 1500° F. when said partially preheated feed oil shale is entrained therein. 
     
     
       9. A process according to claim 8 wherein said hot preheat gas stream is at least in part provided by the flue gas from a ball heater for heating heat carrying solids. 
     
     
       10. A process according to claim 5 wherein a portion of said low Btu gas is combusted with combustion air in said ball heater to heat said heat carrying solids. 
     
     
       11. A process according to claim 5 wherein said low Btu gas contains water and said water is separated therefrom prior to introduction into said incineration zone to provide a moisture free low Btu gas. 
     
     
       12. A process according to claim 11 wherein water is separated from said low Btu gas by cooling said low Btu gas to below 150° F. and separating said condensed water therefrom to form a cooled moisture free low Btu gas. 
     
     
       13. A process according to claim 12 wherein said cooled moisture free low Btu gas is heated prior to introduction into said incineration zone to a temperature of about 400° F. 
     
     
       14. A process according to claim 13 wherein said moisture free cooled low Btu gas is heated with said combustion heat prior to introduction into said incineration zone. 
     
     
       15. A process according to claim 10 wherein at least a portion of said combustion heat is used to preheat said combustion ball heater combustion air and said incinerator combustion air to temperatures of about 800° F. to 900° F. 
     
     
       16. A process according to claim 5 wherein sufficient low Btu gas and combustion air are combusted in said incineration zone to maintain a zone temperature of about 1400° F. 
     
     
       17. A process according to claim 4 wherein the substantially hydrocarbon free waste gas is further treated to remove sulfur and entrained fines prior to venting to the atmosphere. 
     
     
       18. In a process for preheating raw oil shale wherein the raw oil shale is first partially preheated to a temperature of about 200° F. to 400° F. by entrainment in a first gas stream and wherein the partially heated oil shale is separated from the gas stream for further preheating and pyrolysis and wherein said separated gas stream which contains hydrocarbons released from said partially preheated oil shale is vented to the atmosphere, the improvement comprising: entraining said oil shale in a combustible gas stream having a sufficient temperature to heat said oil shale to about 200° F. to 400° F.; and   utilizing said combustible gas stream after separation from said partially preheated oil shale as a combustion fuel whereby said hydrocarbons released from said oil shale into said combustible gas stream are combusted with said gas stream and not vented to the atmosphere.   
     
     
       19. In a staged preheating process for preheating oil shale, wherein raw feed oil shale is initially entrained in a first gas stream to partially preheat the feed oil shale to temperatures of between about 200° F. to 400° F., said partially preheated feed oil shale being separated from said first gas stream and entrained in a second gas stream to preheat the feed oil shale to temperatures of between about 400° F. and 650° F., said preheated feed oil shale being separated from said second gas stream and passed to a retort for pyrolysis, and wherein said first gas stream contains hydrocarbons released from said feed oil shale and said second gas stream contains hydrocarbons released from said feed oil shale, said preheating process further including combustion in an incineration zone of said hydrocarbons in said second gas stream after separation from said preheated spent shale with said first gas stream being vented to the atmosphere; wherein the improvement comprises: providing a first gas stream having a low Btu heating value for entraining said raw feed oil shale to partially preheat the feed oil shale; and   separating the low Btu first gas stream from said partially preheated feed oil shale, said first gas stream containing said hydrocarbons released from the feed oil shale; and   combusting said first gas stream to provide heat whereby said hydrocarbons in said first gas stream are not vented to the atmosphere.   
     
     
       20. In a staged oil shale preheat apparatus having a series of connected lift pipes for serially preheating oil shale to temperatures of between 400° F. and 650° F. by entrainment in hot gas streams, wherein one or more lift pipes are provided for partially preheating the oil shale to temperatures of between 200° F. and 400° F. and wherein means are provided for separating the partially preheated oil shale from the partial preheat entraining gas stream and venting said gas stream to the atmosphere, said gas stream including entrained hydrocarbons released from said oil shale and wherein means are provided for transferring the partially preheated oil shale to further preheating wherein the improvement comprises: means for producing a substantially oxygen free combustible gas;   means for introducing said combustible gas as said partial preheat entraining gas stream in said partial preheat lift pipes;   means for separating said combustible gas with hydrocarbons entrained therein from said partially preheated oil shale; and   means for combusting said combustible gas to incinerate said entrained hydrocarbons whereby said hydrocarbons are not vented to the atmosphere.   
     
     
       21. An improved apparatus according to claim 20 wherein said means for producing a substantially oxygen free combustible gas includes gasifier means for gasifying carbonaceous material to form a low Btu gas containing hydrogen and water. 
     
     
       22. An improved apparatus according to claim 21 wherein means are provided for separating water from said low Btu gas prior to combustion thereof to form a substantially dry low Btu gas. 
     
     
       23. An improved apparatus according to claim 22 wherein means are provided for combusting at least a portion of the dry low Btu gas, with said released hydrocarbons entrained therein, in a ball heater adapted to heat ceramic balls which are used as the heat transfer medium in oil shale pyrolysis. 
     
     
       24. An improved apparatus according to claim 22 wherein means are provided for combusting at least a portion of the dry low Btu gas, with said released hydrocarbons entrained therein, in an incinerator to incinerate hydrocarbons in flue gases vented from other higher temperature lift pipes in the preheat apparatus which are introduced into said incinerator. 
     
     
       25. A process according to claim 1 wherein said partially preheated oil shale is further preheated to a temperature of between about 400° F. to 600° F. after separation from said partially cooled gas stream.